Identification of a Small Molecule That Inhibits the Interaction of LPS Transporters LptA and LptC

The need for novel antibiotics has become imperative with the increasing prevalence of antibiotic resistance in Gram-negative bacteria in clinics. Acting as a permeability barrier, lipopolysaccharide (LPS) protects Gram-negative bacteria against drugs. LPS is synthesized in cells and transported to the outer membrane (OM) via seven lipopolysaccharide transport (Lpt) proteins (LptA-LptG). Of these seven Lpt proteins, LptC interacts with LptA to transfer LPS from the inner membrane (IM) to the OM, and assembly is aided by LptD/LptE. This interaction among the Lpt proteins is important for the biosynthesis of LPS; therefore, the Lpt proteins, which are significant in the assembly process of LPS, can be a potential target for new antibiotics. In this study, a yeast two-hybrid (Y2H) system was used to screen compounds that could block LPS transport by inhibiting LptA/LptC interaction, which finally disrupts the biosynthesis of the OM. We selected the compound IMB-0042 for this study. Our results suggest that IMB-0042 disrupts LptA/LptC interaction by binding to both LptA and LptC. Escherichia coli cells, when treated with IMB-0042, showed filament morphology, impaired OM integrity, and an accumulation of LPS in the periplasm. IMB-0042 inhibited the growth of Gram-negative bacteria and showed synergistic sensitization to other antibiotics, with low cytotoxicity. Thus, we successfully identified a potential antibacterial agent by using a Y2H system, which blocks the transport of LPS by targeting LptA/LptC interaction in Escherichia coli.